This invention relates to fiber optic cables, the fabrication of such cables, and in particular to such cables which are useful in graphic imaging systems such as phototypesetters.
During the last 30 years, numerous so-called second generation phototypsetters have been marketed. These machines flash-illuminate characters positioned upon a whirling character disk or drum, and the resulting optical image is projected by a lens system upon a photosensitive film. The size of the characters are changed by means of moving zoom lenses or the like or by rotating a lens turret to position various lenses at the optical projection axis. The characters are sequentially recorded upon the photosensitive film by mechanically scanning such film. The film carriage may be moved relative to the optical axis, the projection lenses may be moved relative to the film platen, the whirling character disk may be moved relative to the film platen, or various combination of the foregoing may be employed to sequentially project the characters upon the film to form a line of characters. Generally, the projection lens carriage assemblies are relatively heavy and bulky, as is the drum or disk bearing the images of the characters to be projected. Also, changes in the fonts involve manual replacement of the character disks, or film strips mounted upon a drum. Additionally, the electro-mechanical stepping devices for producing the above mentioned scanning motions are also relatively bulky and cumbersome. The speed of second generation machines is limited by the output carriage escapement speed and by character access time determined by the rotational speed of the font disk.
So-called third generation phototypesetters were introduced in the 1960s, most of which utilize cathode ray tubes for generating the characters upon the faces of the tubes. These character images are thereafter optically projected upon the film. In contrast with the components of the second generation machines, the electron beam is essentially unhindered by inertia and the computer codes thus may actuate the beam at much higher speeds than those obtainable by the second generation machines. Laser generated light beams have also been employed rather than cathode ray tubes. Many font families may be generated by these machines since the character generating codes may be densely packed during recordation upon magnetic storage media, such as floppy disks. Also, the character size may be electronically changed by changing the length of the beam traces making up the character components (See FIG. 1 of U.S. Pat. No. 3,952,311).
The result of the foregoing is that these machines have higher speeds, and greater flexibility in the character shapes and sizes produced. However, the third generation machines are usually considerably more expensive than the second generation machines; in 1979, they typically sold for $40,000 on up. In contrast, second generation machines in 1979 were marketed for around $10,000.
A fourth generation typesetter is disclosed in U.S. patent application Ser. No. 181,312 filed Aug. 25, 1980, now U.S. Pat. No. 4,342,504 by Peter Ebner, for an LED-fiber-optic character printer. The fourth generation typesetter can be marketed for about $10,000, and yet it has the speed and flexibility of the third generation machines. These results have been accomplished by providing a flexible ribbon of a small number of fiber optic filaments. Each filament is illuminated by one of a matrix of light emitting diodes (LEDs) and has its output end positioned within a printing head. The printing head has at least one relatively short linear array of fiber optic filaments embedded therein. Means are provided for causing the head to scan across the photosensitive material and to record a line of type thereon with light provided by selective energizing of the LEDs. The invention claimed in the above application utilizes a loop of fiber optic cable comprising fiber optic filaments mounted upon a belt-like substrate. This flexible fiber optic loop enables rapid scanning by the printing head with a fiber optic cable containing a drastically reduced number of fiber optic filaments, for example, 128, in contrast with the thousands of filaments called for by prior cables in general usage. With use, it has been found that continued flexing of the fiber optic cable causes stress of the fiber optic filaments.
A principle object of the present invention is to provide an improved fiber optic cable and a method and apparatus for producing it. Construction of a fiber optic cable and LED matrix assembly in which microscopic fiber optic filaments are connected to very small light emitting diodes is extremely difficult. The filaments themselves are fragile and subject to breakage. Light emitting diodes have a limitation as to their intensity, and for that reason it is extremely important to place each fiber optic filament input end as near as possible to the most intense emitting area of an LED. Placement of a 0.002 inch fiber filament end upon a roughly 0.005 inch square or circular emitting area requires precision placement within 0.001 inches of the target.
An object of this invention is to provide a method and apparatus for the precision placement of fiber optic filaments at the maximum light emitting areas of each LED.
The fourth generation phototypesetter is to be a mass produced machine and, as with all massed produced, economically viable machines, parts included in the machine must also be mass produced and must be functionally identical. A photo-optic cable to be used in such a machine with a small number of fiber optic filaments and light emitting diodes must respond in the same way as the part which it is replacing.
It is a further object of the invention to provide a relatively inexpensive method and apparatus of producing operationally identical cables having a number of fragile fiber optic filaments, each precisely associated within an LED matrix, and a printing head, positioned in such a manner that the fibers see little stress.